Test Bench: Onkyo TX-SR605 A/V Receiver

As seems usual for Onkyo, the TX-SR605 showed just how technically accomplished mass-produced electronics can be today, with perfectly flat frequency response and perfect D/A linearity to -90 dB (and beyond). Both are as good results as I've measured, and while my memory isn't infallible, I believe this to be the first time these two particular aces have been drawn by the same unit. The Onkyo's S/N results on our dithered-silence tests were slightly "better-than-perfect" in theoretical terms (-75.6 being the pure-dither result), which suggests a slight shortfall of its LSB (lowest significant bit) magnitude; probably not meaningful in any audible sense. (Like most units that measure similarly, the error was greater for Dolby Digital than for PCM digital signals; I've never been able to figure out why this should be, but have observed it more than a few times.)

Power results were fairly typical for a mid-market A/V receiver. The TX-SR605 met its single-channel and stereo specs handily enough, but fell short when 5 or 7 channels were stressed simultaneously, and protected itself to about one-third power, presumably via current-limiting circuitry, when asked to do so for more than a few hundred milliseconds. This almost certainly has very little audible impact - the receiver played 7 channels happily enough at 1 dB short of clipping for many minutes at a time. This design approach, which we see often, probably reflects the manufacturer's attempt to hold down power-supply costs and is sensible enough in real-world terms, where 5 or 7 channels probably never demand full power simultaneously for more than a tenth of a second at a time.

DOLBY DIGITAL PERFORMANCE

All data was obtained from various test DVDs using 16-bit dithered test signals, which set limits on measured distortion and noise performance. Reference input level is -20 dBFS, and reference output is 1 watt into 8 ohms. Volume setting for reference level was 75. All level trims at zero, except for subwoofer-related tests, all speakers were set to "large," subwoofer on. All are worst-case figures where applicable.

*With more than four channels stressed to clipping simultaneously for durations greater than a few hundred milliseconds, the TX-SR605 protected itself to about one-third power, presumably via current-limiting circuitry. Reducing drive level for a few minutes, or power-cycling the unit, restored normal operation.